Im trying to make my object track another, so far my code gets all the relavent info but im not sure what to do with it. I cant make the simple one, if x is less than x2 go left... Because my game objects dont move left or right, they rotate. So.. object ax ||| pos(10,10) object bx ||| i want object bx to track ax, but the problem is, because i can only rotate object bx, i need someway, to work out which way to rotate it, to make it face object ax, then i can move towards it. I hope you can help. Thanks alot all. Cya

First, a comment: This sort of problem has been asked and answered many times in the Maths & Physics forum. You might first want to check the archives of that forum in the future, if you have a question of this type (that goes for everyone else as well). For now though, here is the answer you seek...


There are two parts to this problem:

1) Determine the smallest angle between the two objects; and,
2) Determine the direction to rotate through that angle (positive or negative sense).

First, define two vectors, A andB , being the vectors from the origin to the objects a and b respectively. Then,

Part 1)

              A  . B   theta = cos-1(------)             |A|  |B|   

Part 2)
The cross product of two vectors is orthogonal to the plane that they define and is a signed operation... meaning that if you reverse the two vectors, you get the negative of the value.

The cross product operation follows a right hand rule so if you want to work out the direction for a rotation from b to a, take the cross product,

B  x A    

If it is positive, then rotate theta radians in the positive direction (counterclockwise), else if it is negative, rotate theta radians in the negative (clockwise) direction.

Cheers,

Timkin

[edited by - Timkin on April 27, 2002 9:56:12 PM]

also, if you want to extend your tracking algo. you can implement an intercept personality to your tracking unit. basically you track a point ahead of the target based on the current movement. you would use the last few positions and extrapolate the next position. the difficulty though lies in the correct extrapolation. a simple scheme uses the current speed in a linear fashion and tries to predict the best route based on that information. this may sound like a ramble and be somewhat confusing, but it is merely to get your creative juices flowing once you get the standard follow a target routine working.

Yep... several people (including myself) just discussed this very idea in this thread:

Take a read and see what you think.

Cheers,

Timkin

[edited by - Timkin on April 28, 2002 8:36:47 PM]